1. Field of the Invention
The present invention relates to an ultrasonic diagnosing apparatus for imaging organs, bones, etc. within a living body by transmitting and receiving ultrasonic waves to generate ultrasonic images to be used for diagnosis.
2. Description of a Related Art
In an ultrasonic diagnosing apparatus to be used for medical application, normally, an ultrasonic probe including plural ultrasonic transducers having transmitting and receiving functions of ultrasonic waves is used. By using such ultrasonic probe, an object to be inspected is scanned by an ultrasonic beam formed by compounding the plural ultrasonic waves and the ultrasonic echoes reflected inside the object are received, and thereby, image information on the object is obtained based on the intensity of the ultrasonic echoes. Furthermore, two-dimensional or three-dimensional images of the object are reproduced based on the image information.
By the way, when ultrasonic beams are transmitted from the ultrasonic probe to the human body, the amplitudes of the ultrasonic echoes reflected at the interfaces between soft tissues such as muscles and hard tissues such as bones become large, and therefore, these interfaces are displayed in high brightness in an ultrasonic image. On the other hand, because the ultrasonic echoes from inside and behind the hard tissues are weak, it is extremely difficult to visually recognize the image of the hard tissues such as bones, tendons, nucleus pulposus, etc. while separating those from the soft tissues such as muscles.
As a related technology, Japanese Patent Application Publication JP-P2001-170046A discloses a living tissue property diagnosing apparatus arranged so as to perform an accurate diagnosis regardless of a target of measurement. In the living tissue property diagnosing apparatus, signal analysis means includes pulse width setting means for setting a signal pulse width of an electric signal obtained from a received ultrasonic pulse, region extracting means for extracting plural regions of signal that are different from each other at least in parts of the regions from the range of the set signal pulse width, waveform characteristic value calculating means for calculating a predetermined waveform characteristic value in each of the extracted regions, difference computing means for computing the difference between the calculated waveform characteristic values, and corresponding time determination means for relating a result of the difference computation to a position of the living tissue from which the ultrasonic pulse has been generated by relating the result of the difference computation to a reception time of the ultrasonic pulse. As the waveform characteristic values, peak frequencies, center frequencies, bandwidth ratios, 6dB-reduced frequencies, primary moment, secondary moment, etc. are used. However, extracting plural regions of signal that are different from each other at least in parts of the regions from the range of the set signal pulse width corresponds to utilizing the difference between information in a depth direction within the object, and therefore, axial resolution is degraded. That is, differential characteristics in the depth direction are obtained and it cannot be a characteristic indicating a feature at one point.
Further, Japanese Patent Application Publication JP-P2000-5180A discloses an acoustic impedance measurement apparatus that is practicable and capable of displaying an acoustic impedance of a target of measurement in images with high resolution at high speed. This acoustic impedance measurement apparatus includes frequency converter means for obtaining frequency characteristics of ultrasonic reply signals, parameter extracting means for extracting a predetermined parameter from the frequency characteristics, and acoustic impedance calculating means for calculating the acoustic impedance of the target of measurement by using the extracted parameter. In the acoustic impedance measurement apparatus, in order to measure the acoustic impedance of the target of measurement, broadband pulse signals such as trapezoidal pulses and rectangular pulses are used. Such pulse signals are broadband, but include only unique frequency components determined depending on their own waveforms and the ratio between the components are limited.
Furthermore, Japanese Patent Application Publication JP-A-5-42147 discloses a lithotrity degree measurement apparatus in calculus spallation treatment within a living body for performing treatment with shockwave while observing the lithotrity condition as image information. This lithotrity degree measurement apparatus includes means for obtaining an amplitude value by converting received reflection waves into an electric signal, means for outputting a maximum amplitude value from the amplitude value of the electric signal, means for converting the signal into a frequency signal by performing frequency analysis of the electric signal, means for comparing the maximum amplitude value with a preset amplitude value, and means for calculating a predetermined characteristic value from the frequency signal if the comparing means judges that the maximum amplitude value is larger than the preset amplitude value. However, the information obtained by the apparatus is only the lithotrity degree and information on the tissues within the living body cannot be obtained.
Further, Japanese Patent Application Publication JP-A-10-179589 discloses ultrasonic image processing method and apparatus for performing image processing on tissues and body fluids on the basis of response frequencies which are different from the transmitting frequencies, specifically, harmonic echoes of the transmitting fundamental frequency and come back from the tissues or body fluids. However, such harmonic echoes are not necessarily generated from any tissue at sufficient amplitudes, and, although the harmonic echoes generated in the tissues are received, linear frequency response characteristics of the tissues are not thereby obtained.